Wet-type multi-plate clutch

ABSTRACT

In a wet-type multi-plate clutch comprising an externally-toothed plate and an internally-toothed plate each of which is formed by adhering a friction material on a core plate and in which torque is transmitted by engaging the externally-toothed plate and the internally-toothed plate, the friction materials are adhered on opposed surfaces of the externally-toothed plate and the internally-toothed plate which are opposed to each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wet-type multi-plate clutch used in aclutch and/or a brake of an automatic transmission (AT) of a vehicle.More particularly, the present invention relates to an improvement infriction surfaces of an internally- toothed plate and anexternally-toothed plate.

2. Description of the Related Art

In the past, wet-type multi-plate clutches were provided with separatorplates as externally-toothed plates and friction plates asinternally-toothed plates obtained by adhering friction materials oncore plates and were designed to transmit torque by engaging theexternally-toothed plates with the internally-toothed plates.

Further, most of friction heat generated by these plates upon engagementof the clutch is transferred to the externally-toothed plates or theinternally-toothed plates to which the friction materials are notadhered to be dispersed, since the friction material has a predeterminedadiabatic property.

In the past, a wet-type multi-plate clutch comprising friction plates asinternally-toothed plates on both surfaces of which friction materialsare adhered,, as shown in FIG. 1 of Japanese Patent ApplicationLaid-open No. 11-141570 (1999), has been known. Further, a platearrangement of one-surface alternately adhering type in which thefriction materials are adhered on surfaces of the internally-toothedplates and the externally-toothed plates which are not opposed to eachother, respectively, is also known.

Although a plate thickness of the externally-toothed plate can beincreased to increase a dispersed heat amount in order to enhance theadiabatic property, if the plate thickness is increased, an axial lengthof the plate is also increased, thereby arising a new problem that theclutch cannot be designed to have a compact size. To avoid this, therehas been proposed a clutch of one-surface alternately adhering type inwhich the friction materials are adhered alternately on one-surfaces ofthe externally-toothed plates and the internally-toothed plates so as todisperse the friction heat from both of the externally-toothed platesand the internally-toothed plates.

However, in the clutch comprising the plates of one-surface alternatelyadhering type, since the friction heat is generated only on the singlesurface of each plate, unbalance of heat is caused between both surfacesof each plate to deform the plate. Consequently, a bad influence will beaffected upon the endurance and the friction property of the frictionmaterial. Further, during an idle rotation of the clutch, since axialloads are imbalanced between front and rear surfaces of the plate, therearises a problem that it is difficult to maintain a clearance betweenthe internally-toothed plate and the externally-toothed plate constant,thereby increasing idle rotation drag torque.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a wet-typemulti-plate clutch in-which unbalance of heat on each plate can besuppressed by absorbing friction heat by means of both surfaces of eachexternally-toothed plate and each internally-toothed plate, and, in anidle rotation of the clutch, separation between the externally-toothedplate and the internally-toothed plate is improved.

To achieve the above object, the present invention provides a wet-typemulti-plate clutch comprising an externally-toothed plate and aninternally-toothed plate each of which is formed by adhering a frictionmaterial onto a core plate and in which torque is transmitted byengaging the externally-toothed plate with the internally-toothed plateand wherein the friction materials are adhered on opposed surfaces ofthe externally-toothed plate and the internally-toothed plate which areopposed to each other.

According to the wet-type multi-plate clutch as mentioned above, thefollowing advantages can be obtained.

Since the friction materials are adhered on both surfaces of theexternally-toothed plate and of the internally-toothed plate, frictionheat can be absorbed at the both surfaces of the plates to reduce theunbalance of heat on each plate, and further, during an idle rotation ofthe clutch, separation between the externally-toothed plate and theinternally-toothed plate can be improved.

By setting a thickness of the internally-toothed plate to become greaterthan a thickness of the externally-toothed plate, heat dispersingproperties of the externally-toothed plate and the internally-toothedplate can be made more uniform, thereby enhancing the heat resistingability. The reason is that the externally-toothed plate is engaged withan element such as a clutch drum or a transmission case, having a heatcapacity greater than that of a clutch hub with which theinternally-toothed plate is engaged.

Further, by increasing a thickness of each tooth of theinternally-toothed plate, face pressure between teeth at a fittingregion between the internally-toothed plate and the hub can be reduced.The reason is that, generally, in comparison with a fitting region ofthe externally-toothed plate, the fitting region of theinternally-toothed plate having a smaller spline diameter tends toincrease the face pressure between the teeth.

Similarly, since a surface area of the friction surface of the frictionmaterial of the internally-toothed plate can be increased more than acorresponding surface area of the externally-toothed plate, heat loadsapplied to the externally-toothed plate and the internally-toothed platecan be made more uniform, thereby enhancing the adiabatic property. Inthis case, the surface area of the friction material of theinternally-toothed plate can be increased and the thickness of theexternally-toothed plate can be increased, thereby making heat absorbingamounts of the internally-toothed plate and the externally-toothed platemore uniform.

Furthermore, by designing so that the friction materials are adheredasymmetrically on the front and rear surfaces of the externally-toothedplate and the internally-toothed plate, heat generating positions aredifferentiated between the front and rear surfaces in a radialdirection, with the result that heat load to the friction material canbe reduced.

The word “internally-toothed plate” used herein means a plate providedat its inner diameter side with spline teeth and mounted, for a slidingmovement in an axial direction, on a hub of a wet-type multi-plateclutch at an inner diameter side thereof; whereas the word“externally-toothed plate” means a plate provided at its outer diameterside with spline teeth and mounted, for a sliding movement in an axialdirection, on and spline-engaged with a clutch case of the wet-typemulti-plate clutch at an inner diameter side thereof. These plates mayfunctionally differ from a “separator plate” and a “friction plate”which are used in a general sense.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing externally-toothed plates andinternally-toothed plates according to a first embodiment of the presentinvention in detail.

FIG. 2 is a sectional view showing externally-toothed plates andinternally-toothed plates according to a second embodiment of thepresent invention in detail.

FIG. 3 is a sectional view showing externally-toothed plates andinternally-toothed plates according to a third embodiment of the presentinvention in detail.

FIG. 4 is a sectional view showing externally-toothed plates andinternally-toothed plates according to a fourth embodiment of thepresent invention in detail.

FIG. 5 is a sectional view showing externally-toothed plates andinternally-toothed plates according to a fifth embodiment of the presentinvention in detail.

FIG. 6 is an axial partial sectional view for explaining a fundamentalarrangement of a wet-type multi-plate clutch to which variousembodiments of the present invention can be applied.

DESCRIPTION OF THE EMBODIMENTS

Now, various embodiments of the present invention will be fullyexplained with reference to the accompanying drawings. Incidentally, inthe drawings, the same elements or part will be designated by the samereference numerals.

FIG. 6 is an axial partial sectional view for explaining a fundamentalarrangement of a wet-type multi-plate clutch to which variousembodiments of the present invention can be applied. Incidentally,internally-toothed plates and externally-toothed plates according to afirst embodiment of the present invention are mounted to the clutch.

The wet-type multi-plate clutch 10 comprises a substantially cylindricaldrum or clutch case 1 having an axial open one end, a hub 4 arrangedwithin the interior of the clutch case 1 and rotated coaxially relativeto the clutch case, a plurality of annular externally-toothed plates 22mounted to an inner periphery of the clutch case 1 via splines 8 for asliding movement in an axial direction, and a plurality of annularinternally-toothed plates 23 mounted to an outer periphery of the hub 4via splines 5 and alternately arranged with the externally-toothedplates 22 in the axial direction; friction materials are adhered on theinternally-toothed plates.

The wet-type multi-plate clutch 10 further includes a piston 6 forurging and engaging the externally-toothed plates 22 and theinternally-toothed plates 23, a backing plate 7 provided on the innerperiphery of the clutch case 1 and adapted to hold theexternally-toothed plates 22 and the internally-toothed plates 23 in afixed condition at an axial one end of the clutch, and a stop ring 17for holding the backing plate.

As shown in FIG. 6, the piston 6 is mounted within a closed end portionof the clutch case 1 for a sliding movement in the axial direction. AnO-ring 9 is disposed between an outer peripheral surface of the piston 6and an inner surface of the clutch case 1. Further, a seal member (notshown) is also interposed between an inner peripheral surface of thepiston 6 and an outer peripheral surface of a cylindrical portion (notshown) of the clutch case 1. Accordingly, an oil-tight hydraulic chamber11 is defined between an inner surface of the closed end portion of theclutch case 1 and the piston 6.

On both surfaces of the internally-toothed plate 23 held by the hub 4for axial sliding movement, friction materials 25 having a predeterminedcoefficient of friction are secured. Further, friction materials 24 aresecured to both surfaces of the externally-toothed plate 22. Further,lubricating oil supplying ports 13 extending in a radial direction areformed in the hub 4 to flow lubricating oil from the inner diameter sideto the outer diameter side of the wet-type multi-plate clutch 10.

In the wet-type multi-plate clutch 10 having the above-mentionedconstruction, the clutch is engaged (tightened) and disengaged(released) in the following manner. FIG. 6 shows a clutch releasedcondition in which the externally-toothed plates 22 are separated fromthe internally-toothed plates 23. In this released condition, by abiasing force of a return spring (not shown), piston 6 abuts against theinner surface of the closed end portion of the clutch case 1.

From this condition, to engage or tighten the clutch, hydraulic pressureis supplied into the hydraulic chamber 11 defined between the piston 6and the clutch case 1. As the hydraulic pressure is increased, thepiston 6 is shifted to the right in FIG. 6 in opposition to the biasingforce of the return spring (not shown), thereby firmly contacting theexternally-toothed plates 22 with the internally-toothed plates 23. Inthis way, the clutch is engaged.

After the engagement, to disengage the clutch again, the hydraulicpressure is released from the hydraulic chamber 11. When the hydraulicpressure is released, the piston 6 is shifted by the biasing force ofthe return spring (not shown) until it abuts against the inner surfaceof the closed end portion of the clutch case 1. In this way, the clutchis released or disengaged.

First Embodiment

FIG. 1 is a sectional view showing externally-toothed plates 22 andinternally-toothed plates 23 of a wet-type multi-plate clutch accordingto a first embodiment of the present invention in detail. Pluralexternally-toothed plates 22 are arranged at a predetermined pitch alongthe axial direction, and friction materials 25 are adhered on bothsurfaces of each externally-toothed plate via an adhesive or the like atinnermost diameter side thereof. In each of various embodiments shown inFIGS. 1 to 5, a clutch released condition is shown. That is to say, inthis condition, the internally-toothed plates are not engaged with theexternally-toothed plates.

Further, plural internally-toothed plates 23 are arranged at apredetermined pitch along the axial direction, and friction materials 24are adhered on both surfaces of each externally-toothed plate via anadhesive or the like at outermost diameter side thereof. As shown, theexternally-toothed plates 22 and the internally-toothed plates 23 havesubstantially the same axial thickness and are arranged alternatelyalong the axial direction.

As can be seen from FIG. 1, with respect to each of two outermost axialplates among the plural externally-toothed plates 22, the frictionmaterial 25 is adhered on only one surface of the plate which is opposedto the internally-toothed plate 23. Further, with respect to other(intermediate) externally-toothed plates 22, the friction materials 25are adhered on both axial surfaces of each plate. The reason is thatboth surfaces of the intermediate externally-toothed plates 22 areopposed to the internally-toothed plates 23.

To the contrary, the friction materials 24 are provided on both surfacesof all of the internally-toothed plates 23. Thus, the friction materials24 are adhered all surfaces of the internally-toothed plates 22 opposedto the externally-toothed plates 22 including the outermostexternally-toothed plates 22.

An inner diameter side edge 24 a of each friction material 24 providedon the internally-toothed plate 23 is arranged not to interfere with anouter diameter side edge 25 a of each friction material 25 provided onthe externally-toothed plate. That is to say, a predetermined clearanceis formed between the edge 24 a and the edge 25 a along a radialdirection. Accordingly, the friction materials 24 do not interfere withthe friction materials 25 upon engagement of the clutch.

Further, a radial width of the friction material 24 is slightly smallerthan that of the friction material 25. Thus, a friction surface areaslidingly contacting with the friction material in theinternally-toothed plate is greater than that in the externally-toothedplate.

Second Embodiment

FIG. 2 is a sectional view showing externally-toothed plates 22 andinternally-toothed plates 23 according to a second embodiment of awet-type multi-plate clutch of the present invention in detail. Thefundamental construction of the second embodiment is similar to that ofthe first embodiment.

In the second embodiment, the friction materials 24 are adhered on onlyone-surfaces of the externally-toothed plates 22 directed toward thesame direction, and the friction materials 25are adhered on onlyone-surfaces of the internally-toothed plates 23 directed toward thesame direction. As can be seen from FIG. 2, the arrangement is ofone-surface alternately adhering type in which the friction material 24and the friction material 25 are provided on the opposed surfaces,respectively. The externally-toothed plates 22 and theinternally-toothed plates 23 are arranged alternately along the axialdirection.

Similar to the first embodiment, the inner diameter side edge 24 a ofthe friction material 24 provided on the internally-toothed plate 23 isarranged not to interfere with the outer diameter side edge 25 a of thefriction material 25. That is to say, a predetermined clearance isformed between the edge 24 a and the edge 25 a along the radialdirection. Accordingly, the friction materials 24 do not interfere withthe friction materials 25 upon engagement of the clutch.

Further, a radial width of the friction material 24 is slightly smallerthan that of the friction material 25. Thus, a friction surface areaslidingly contacting with the friction material in theinternally-toothed plate is greater than that in the externally-toothedplate. In order to suppress unbalance of heat due to such differencebetween the friction surfaces areas, as shown, an axial thickness of theinternally-toothed plate 23 is set to be greater than an axial thicknessof the externally-toothed plate 22. Further, the friction materials areadhered asymmetrically on the front and rear surfaces of each of theexternally-toothed plate 22 and the internally-toothed plate 23, withthe result that heat generating positions are differentiated between thefront and rear surfaces of each plate, thereby reducing heat load to thefriction material.

Third Embodiment

FIG. 3 is a sectional view showing externally-toothed plates 22 andinternally-toothed plates 23 according to a third embodiment of awet-type multi-plate clutch of the present invention in detail. Thefundamental construction of the third embodiment is similar to that ofthe first embodiment.

In the third embodiment, a method for adhering friction materialsdiffers from those in the first and second embodiment. A pair offriction materials 31 and 35 are adhered both axial surfaces of theinternally-toothed plate 23 which are opposed to the externally-toothedplates 22. Further, a friction material 33 is adhered only on one axialsurface of each of two externally-toothed plates 22 which are disposedat outermost axial ends, and, with respect to other externally-toothedplates 22 disposed between the two outermost externally-toothed plates,friction materials 33 are adhered on both axial surfaces of each plate.

The friction material 31 is adhered on the internally-toothed plate 23at an outermost diameter side thereof and the friction material 35 isadhered at an innermost diameter side of the internally-toothed plate. Apredetermined radial gap is formed between the friction material 31 andthe friction material 35.

The friction material 33 adhered to the externally-toothed plate 22 isarranged at a middle area in the radial direction and is positioned sothat it is fitted into the gap defined between the friction material 31and the friction material 35 adhered on the internally-toothed plate 23.Predetermined clearances are formed between an inner diameter side edge31 a of the friction material 31 and an outer diameter side edge 33 a ofthe friction material 33 and between an outer diameter side edge 35 a ofthe friction material 35 and an inner diameter side edge 33 b of thefriction material 33.

Accordingly, since the friction material 33 is fitted into the gapbetween the friction material 31 and the friction material 35, thesefriction materials do not interfere with each other, thereby notobstructing the engagement of the clutch.

Further, a radial width of the friction material 31 is substantially thesame as a radial width of the friction material 35; whereas, a radialwidth of the friction material 33 is smaller than those of the frictionmaterials 31 and 35. Since the friction materials 31 and 35 are adheredon the internally-toothed plate 23, the friction surface area of theexternally-toothed plate 22 is greater than the friction surface area ofthe internally-toothed plate 23 by about two times or more. Thus, thefriction surface area of the externally-toothed plate against which thefriction material is slidingly contacted is greater than that of theinternally-toothed plate. In order to suppress unbalance of heat due tosuch difference between the friction surfaces areas, as shown, an axialthickness of the externally-toothed plate 23 is set to be greater thanan axial thickness of the internally-toothed plate 22.

By increasing the thickness of the externally-toothed plate more thanthe thickness of the internally-toothed plate in this way, heatdispersing properties of the externally-toothed plate and theinternally-toothed plate can be made uniform, thereby enhancing the heatresisting ability. The reason is that the externally-toothed plate isengaged with an element such as a clutch drum or a transmission case,having a heat capacity greater than that of a clutch hub with which theinternally-toothed plate is engaged.

Fourth Embodiment

FIG. 4 is a sectional view showing externally-toothed plates 22 andinternally-toothed plates 23 according to a fourth embodiment of awet-type multi-plate clutch of the present invention in detail. Thefundamental construction of the fourth embodiment is similar to that ofthe first embodiment.

In the fourth embodiment, friction materials 41 and 45 are adhered on anaxial one surface of each of the internally-toothed plates 23. Further,a friction material 43 is adhered on the other axial surface of eachinternally-toothed plate. Further, a pair of friction materials 41 and45 is adhered on an axial one surface of each of the externally-toothedplates 23, and a friction material 43 is adhered on the other axialsurface of each externally-toothed plate.

The friction materials 41 are adhered on the externally-toothed plate 22and the internally-toothed plate 23 at their outermost diameter sides,whereas, the friction materials 45 are adhered at their innermostdiameter sides. A predetermined radial gap is formed between thefriction material 41 and the friction material 45. Further, the frictionmaterials 43 are adhered on the externally-toothed plate 22 and theinternally-toothed plate 23 at their substantially middle areas thereofin the radial direction.

As shown in FIG. 4, the pair of friction materials 41 and 45 is adheredon one surface of one of two externally-toothed plates 22 disposed atendmost positions in the axial direction, and the friction material 43is adhered on one surface of the other externally-toothed plate 22.Intermediate externally-toothed plates 22 disposed between the endmostexternally-toothed plates have the same constructions, and, regardingthese intermediate plates, the pair of friction materials 41 and 45 isadhered on one surface of each plate and the friction material 43 isadhered on the other surface of each plate.

Between the friction materials 41 and 45 adhered at plural positions inthe radial direction, a gap is defined, into which the friction material43 adhered at the intermediate position can be fitted. Accordingly, uponthe engagement of the clutch, as the internally-toothed plate 23 and theexternally-toothed plate 22 approach each other, the friction material43 is fitted into the gap between the friction material 41 and thefriction material 45.

Predetermined clearances are formed between an inner diameter side edge41 a of the friction material 41 and an outer diameter side edge 43 a ofthe friction material 43 and between an outer diameter side edge 45 a ofthe friction material 45 and an inner diameter side edge 43 b of thefriction material 43, so that the friction material 43 can be fittedbetween the friction material 41 and the friction material 45 adhered onthe externally-toothed plate 22 and the internally-toothed plate 23.

Accordingly, if the friction material 41, friction material 45 andfriction material 43 are shifted in the axial direction, since thesefriction materials do not interfere with each other, the engagement ofthe clutch is not obstructed.

Further, the friction material 41 and the friction material 45 havesubstantially the same radial widths; but, the friction material 43 hasa radial width smaller than those of the friction materials 41 and 45.However, since the friction materials 41 and 45 are adhered on theexternally-toothed plate 22 and the internally-toothed plate 23 and thefriction materials 43 are adhered on the externally-toothed plate 22 andthe internally-toothed plate 23, upon the engagement of the clutch, thefriction surface area of the externally-toothed plate 22 issubstantially the same as that of the internally-toothed plate 23. Thus,since it is not necessary to suppress the unbalance of heat due to thedifference between friction surface areas, as shown, an axial thicknessof the internally-toothed plate 23 can be substantially the same as thatof the externally-toothed plate 22. Further, since the frictionmaterials are adhered asymmetrically on the front and rear surfaces ofthe externally-toothed plate 22 and the internally-toothed plate 23, theheat generating positions are differentiated between the front and rearsurfaces, thereby reducing the heat load to the friction material.

Fifth Embodiment

FIG. 5 is a sectional view showing externally-toothed plates 22 andinternally-toothed plates 23 according to a fourth embodiment of awet-type multi-plate clutch of the present invention in detail. Thefundamental construction of the fifth embodiment is similar to that ofthe fourth embodiment.

In the fifth embodiment, friction materials 51 and 55 are adhered on anaxial one surface of each internally-toothed plate 23. Further, afriction material 53 is adhered on the other axial surface of eachplate. Further, a pair of friction materials 51 and 55 is adhered on anaxial one surface of each externally-toothed plate 22, and a, frictionmaterial 53 is adhered on the other axial surface of the plate.

The friction materials 51 are adhered on the externally-toothed plate 22and the internally-toothed plate 23 at their outermost diameter sides,whereas, the friction materials 55 are adhered at their innermostdiameter sides. A predetermined radial gap is formed between thefriction material 51 and the friction material 55. Further, the frictionmaterials 43 are adhered on the externally-toothed plate 22 and theinternally-toothed plate 23 at their substantially middle areas thereofin the radial direction.

As shown in FIG. 5, the pair of friction materials 51 and 55 is adheredon one surface of one of two externally-toothed plates 22 disposed atendmost positions in the axial direction, and the friction material 53is adhered on one surface of the other externally-toothed plate 22.Intermediate externally-toothed plates 22 disposed between the endmostexternally-toothed plates have the same constructions, and, regardingthese intermediate plates, the pair of friction materials 51 and 55 isadhered on one surface of each plate and the friction material 53 isadhered on the other surface of each plate.

Between the friction materials 51 and 55 adhered at plural positions inthe radial direction, a gap is defined, into which the friction material53 adhered at the intermediate position can be fitted. Accordingly, uponthe engagement of the clutch, as the internally-toothed plate 23 and theexternally-toothed plate 22 approach each other, the friction material53 is fitted into the gap between the friction material 51 and thefriction material 55.

Predetermined clearances are formed between an inner diameter side edge51 a of the friction material 51 and an outer diameter side edge. 53 aof the friction material 53 and between an outer diameter side edge 55 aof the friction material 55 and an inner diameter side edge 53 b of thefriction material 53, so that the friction material 53 can be fittedbetween the friction material 51 and the friction material 55 adhered onthe externally-toothed plate 22 and the internally-toothed plate 23.

Accordingly, if, the friction material 51, friction material 55 andfriction material 53 are shifted in the axial direction, since thesefriction materials do not interfere with each other, the engagement ofthe clutch is not obstructed.

Further, the friction material 51 and the friction material 55 havesubstantially the same radial widths; but, the friction material 53 hasa radial width smaller than those of the friction materials 51 and 55.However, since the friction materials 51 and 55 are adhered on onesurfaces of the externally-toothed plate 22 and the internally-toothedplate 23 and the friction materials 53 are adhered on the other thesurfaces of externally-toothed plate 22 and the internally-toothed plate23, upon the engagement of the clutch, the friction surface area of theexternally-toothed plate 22 is substantially the same as that of theinternally-toothed plate 23.

Since the externally-toothed plate is engaged with an element such as aclutch drum or a transmission case, having a heat capacity greater thanthat of a clutch hub with which the internally-toothed plate is engaged,by increasing the thickness of the internally-toothed plate more thanthe thickness of the externally-toothed plate, heat dispersingproperties of the externally-toothed plate and the internally-toothedplate can be made uniform, thereby enhancing the heat resisting ability.

Thus, the friction surface area of the internally-toothed plate againstwhich the friction material is, slidingly contacted becomes greater thanthat of the externally-toothed plate. In order to suppress the unbalanceof heat due to such difference between the friction surface areas, asshown, the axial thickness of the internally-toothed plate 23 is greaterthan that of the externally-toothed plate 22.

In the above-mentioned embodiments, the friction materials are adheredasymmetrically on the front and rear surfaces of the core plates of theinternally-toothed plate 23 and the externally-toothed plate 22.Further, the axial thicknesses of the core plates are set so that theheat absorbing capacities at the friction surfaces of theexternally-toothed plate 22 and the internally-toothed plate 23 aresubstantially the same as each other.

Further, the friction materials can be adhered on the internally-toothedplate 23 or the externally-toothed plate 22 at plural positions thereofin the radial direction. By adhering the friction material on theopposed surfaces of the externally-toothed plate 22 and theinternally-toothed plate 23 and by adhering the friction materials onboth surfaces of the externally-toothed plate 22 and theinternally-toothed plate 23, the friction heat can be absorbed at bothsurfaces to reduce the unbalance of heat of the plate, and, during theidle rotation of the clutch, the separation between theexternally-toothed plate 22 and the internally-toothed plate 23 can beimproved.

The friction material may be formed as a ring-shaped element or may beformed by adhering friction material segments. Further, the frictionmaterial may be provided with a lubricating oil passage or an oil grooveas a lubricating oil reservoir. When the friction material segment areadhered to form the friction material, regions defined between thefriction material segments and exposing the core plate can also beexpected to act as oil grooves.

Further, upon the engagement of the wet-type multi-plate clutch, i.e.when both plates are engaged with each other, by setting so that theheat amount generated on the friction surface of the externally-toothedplate becomes equal to the heat amount generated on the friction surfaceof the internally-toothed plate, the heat dispersing properties of bothplates can be made more uniform, thereby enhancing the heat resistingability.

In the internally-toothed plate and the externally-toothed plate,although the friction material adhered at the outer diameter side andthe friction material adhered at the inner diameter side are formed fromthe same material, these friction materials may be formed from differentmaterials. Further, it should be noted that the number of the frictionmaterials provided at plural positions in the radial direction is notlimited to the illustrated number(s), but other numbers of frictionmaterials can be provided.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2006-37922, filed Feb. 15, 2006, which is hereby incorporated byreference herein in its entirety.

1. A wet-type multi-plate clutch comprising an externally-toothed plateand an internally-toothed plate each of which is formed by adhering afriction material on a core plate and in which torque is transmitted byengaging said externally-toothed plate with said internally-toothedplate, wherein: said friction materials are adhered on opposed surfacesof said externally-toothed plate and said internally-toothed plate whichare opposed to each other.
 2. A wet-type multi-plate clutch according toclaim 1, wherein said friction materials are adhered on saidinternally-toothed plate or said externally-toothed plate at a pluralityof positions in a radial direction.
 3. A wet-type multi-plate clutchaccording to claim 1, wherein said friction materials are adheredasymmetrically on front and rear surfaces of said internally-toothedplate and said externally-toothed plate.
 4. A wet-type multi-plateclutch according to claim 1, wherein axial thicknesses of said coreplates of the respective externally-toothed and internally-toothedplates are defined so that heat absorbing capacities at frictionsurfaces of said externally-toothed and internally-toothed plates aresubstantially the same as each other.
 5. A wet-type multi-plate clutchaccording to claim 1, wherein the friction material for engaging at anoutermost diameter side is adhered on said internally-toothed plate. 6.A wet-type multi-plate clutch according to claim 1, wherein a thicknessof said core plate of said internally-toothed plate is greater than athickness of said core plate of said externally-toothed plate.
 7. Awet-type multi-plate clutch according to claim 1, wherein a frictionsurface area of said friction material of said internally-toothed plateis greater than a friction surface area of said friction material ofsaid externally-toothed plate.
 8. A wet-type multi-plate clutchaccording to claim 1, wherein a thickness of said core plate of saidexternally-toothed plate is greater than a thickness of said core plateof said internally-toothed plate.
 9. A wet-type multi-plate clutchaccording to claim 1, wherein, upon engagement of said clutch, a heatamount generated on a friction surface of said externally-toothed plateis equal to a heat amount generated on a friction surface of saidinternally-toothed plate.